Improver containing fuel

ABSTRACT

The invention relates to an improver in the form of a mixture of at least polysiloxane antifoaming agent and at least partially or totally neutralised fat acid. The inventive fuel and additive containing said mixture are also disclosed.

The present invention relates to an additive mixture comprising at leastone polysiloxane antifoam and at least one partially or completelyneutralized fatty acid.

An important component of fuel additive packages is antifoams which areintended to dampen the natural foaming behavior of fuels, in particularon filling, for example during the filling procedure at the gas pump.Polysiloxanes, in particular polysiloxane alkoxylates, are frequentlyused antifoams.

For instance, U.S. Pat. No. 6,093,222 describes antifoam compositionsfor diesel fuels which comprise various polysiloxanes. The polysiloxanesare substituted by long-chain polyether groups, organic polyols,hydrocarbon radicals and/or phenol radicals. However, as a consequenceof the high costs for the production of polysiloxane antifoams, these,in the amount in which they are required to achieve an antifoamperformance, represent a not insignificant cost factor.

WO 95/04117 describes an additive composition which comprises anantifoam and a nitrogen-containing dispersant which burns ashlessly. Thenitrogen-containing dispersant which burns ashlessly is intended toincrease the long-term storage stability of the antifoam. However, thedispersant does not reduce the amount of antifoam required for dampingthe foam formation of a fuel.

It is an object of the present invention to provide an additive mixturewhich exhibits an improved antifoam action in comparison to prior artantifoams.

We have found that this object is achieved by an additive mixturecomprising,

-   -   i) as component A, at least one polysiloxane antifoam and    -   ii) as component B, at least one partially or completely        neutralized fatty acid, a long-chain carboxylic acid, an ester        of such a carboxylic acid or a mixture comprising at least one        of these compounds.

Suitable polysiloxane antifoams are any common antifoams based onpolysiloxane and known to those skilled in the art. Such antifoams aredescribed, for example, in ATC Doc. 52 “Fuel Additives and theEnvironment”.

A preferred antifoam is a polysiloxane of the general formula I

where

-   -   the R radicals are each independently an R¹, R², R³, R⁴ or R⁵        radical where    -   R¹ is an aromatic or saturated aliphatic hydrocarbon radical,    -   R² is an organic polyol,    -   R³ is a polyether radical,    -   R⁴ is a phenol radical,    -   R⁵ is an R² radical, except that some or all of the hydroxyl        groups have been converted to diesters, diethers, acetals and/or        ketals,        w=2+y+2z,    -   y and z are each independently a number from 0 to 2 where the        sum of y and z corresponds to a number from 0 to 2 and    -   w+x+y+z=from 20 to 60.

In R¹, the aromatic or saturated aliphatic hydrocarbon radical ispreferably C₁-C₂₄-alkyl, in particular methyl, ethyl, propyl, isopropyl,butyl, pentyl, hexyl, heptyl, octyl, decyl, dodecyl or stearyl;C₃-C₂₄-cycloalkyl, in particular cyclopropyl, cyclopentyl, cyclohexyl,cyclooctyl or cyclodecyl; C₄-C₂₄-alkylcycloalkyl, in particularmethylcyclohexyl, dimethylcyclohexyl or ethylcyclohexyl; C₆-C₁₀-aryl, inparticular phenyl; or C₇-C₁₈-arylalkyl, in particular methylphenyl,dimethylphenyl or phenylethyl. R¹ is more preferably C₁-C₂₄-alkyl, inparticular methyl.

In R², the organic polyol is preferably a saturated or unsaturated,branched or unbranched, aliphatic hydrocarbon radical having at leasttwo hydroxyl groups which is optionally interrupted by one or moreoxygen atoms. Preference is given to the hydrocarbon radical beingsaturated. The R² radical preferably has a molecular weight of from 100to 700, more preferably from 130 to 650 and in particular of about 400.

The R² radicals are introduced into the polysiloxane framework, forexample, by reacting an unsaturated polyol with a polysiloxane whichcontains hydrogen atoms bonded to silicon. Examples of polyols suitablefor preparing saturated R² radicals include trimethylolpropane monoallylether, ethoxylated pentaerythritol allyl ether, propoxylatedpentaerythritol allyl ether, triisopropanolamine allyl ether,ethoxylated allylsorbitol and 1,3-allyloxypropanediol. An example of apolyol suitable for preparing an unsaturated R² radical is2-butyne-1,4-diol.

R³ is preferably a polyether radical which comprises at least 50% byweight, more preferably at least 75% by weight and in particular 100% byweight, of copolymerized ethylene oxide units. The molecular weight ofR³ is preferably up to 1500, more preferably from 100 to 350.

R⁴ is preferably a phenol radical which is substituted by mono- orpolyunsaturated alkene and/or alkyne radicals. Suitable examples thereofinclude eugenol, vinylphenol, vinylguaiacol and 4-allylphenol.

In the case of preferred polysiloxanes of the formula I, the quotient ofthe number of R¹ groups to the number of R² groups (R¹/R²) is from 3 to19.

Also, in preferred polysiloxanes I, the quotient of the sum of thenumber of R³, R⁴ and R⁵ groups to the number of R² groups[(R³+R⁴+R⁵)/R²] is from 0 to 2.

In a preferred embodiment, component A contains a plurality of differentpolysiloxanes I.

In a particularly preferred embodiment, a polysiloxane I as definedabove is used with a polysiloxane of the general formula I.1

where

-   the R* radicals are each independently an R¹ or R³ radical where R¹    and R³ are each as defined for polysiloxane I;    a=2+c+2d;-   c and d are each independently a number from 0 to 2 and-   a+b+c+d=from 15 to 50,    and/or-   with a polysiloxane of the general formula I.2    where-   R, w, x, y and z are each as defined for polysiloxane I, R² is a    saturated polyol and-   the quotient of the number of R³ groups to the number of R² groups    (R³/R²) and the quotient of the number of R⁴ groups to the number of    R² groups (R⁴/R²) are each greater than 0.

Such polysiloxane combinations are known, for example, from U.S. Pat.No. 6,093,222, which is fully incorporated herein by way of reference.

In preferred polysiloxanes I.1, the quotient of the number of R¹ groupsto the number of R³ groups (R¹/R³) is from 3 to 19.

In preferred polysiloxanes I.2, the quotient (R³/R²) is from 0.25 to 5.

Component B is preferably a fatty acid which has been partially orcompletely neutralized by amines.

Particular preference is given to component B comprising at least onefatty acid salt of the formula II

where

-   R is C₇-C₂₃-alkyl or mono- or polyunsaturated C₇-C₂₃-alkenyl, each    of which are optionally substituted by one or more hydroxyl groups;-   A is C₂-C₈-alkylene;-   Z is C₁-C₈-alkylene, C₃-C₈-cycloalkylene, C₆-C₁₂-arylene or    C₇-C₂₀-arylalkylene;-   m is a number from 0 to 5; and-   x¹, x², x³ and x⁴ are each independently a number from 0 to 24, at    least one x not being 0,-   and optionally at least one further fatty acid RCOOH where R is as    defined above.

Such fatty acid salts II are described, for example, in WO 01/38463,which is fully incorporated herein by way of reference.

The relatively long-chain radical R occurring in the carboxylate anionRCOO— or in the fatty acid RCOOH is, for example, a branched orpreferably linear C₇-C₂₃-, preferably C₁₁-C₂₁-, in particular C₁₅- toC₁₉-alkyl group which may additionally bear hydroxyl groups. Examples ofparent carboxylic acids include octanoic acid, 2-ethylhexanoic acid,nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid (lauricacid), tridecanoic acid, isotridecanoic acid, tetradecanoic acid(myristic acid), hexadecanoic acid (palmitic acid), octadecanoic acid(stearic acid) and eicosanoic acid. The acids mentioned may be ofnatural or synthetic origin. The parent acids of the carboxylate anionsmay also be mixtures of the acids mentioned.

However, preference is given to the relatively long chain radical Roccurring in the carboxylate anion RCOO— or in the fatty acid RCOOHbeing a mono- or polyunsaturated C₇- to C₂₃ radical, in particular amono- or polyunsaturated C₁₁- to C₂₁-, in particular C₁₅- to C₁₉-alkenylgroup which may additionally bear hydroxyl groups. These unsaturatedradicals are preferably linear. Examples of monounsaturated fatty acidsinclude palmitoleic acid, oleic acid and erucic acid. In the case ofpolyunsaturated alkenyl groups, these preferably contain two or threedouble bonds. Examples of parent carboxylic acids include elaidic acid,ricinoleic acid, linoleic acid and linolenic acid. Particularly goodresults are obtained with oleic acid. The parent carboxylic acids of thecarboxylate anions may also be mixtures of such unsaturated carboxylicacids with each other and also with the abovementioned saturatedcarboxylic acids. Examples of such mixtures include tall oil, tall oilfatty acid and rapeseed oil fatty acid. The unsaturated carboxylic acidsmentioned and the mixtures mentioned are generally of natural origin.

The alkylene group A in compounds of the formula II is preferablyderived from appropriate alkylene oxides such as ethylene oxide,1,2-propylene oxide, 1,2-butylene oxide and cis- or trans-2,3-butyleneoxide. However, it may also be 1,3-propylene, 1,4-butylene, 1,6-hexyleneor 1,8-octylene. A may likewise be a mixture of different groupsmentioned. Particular preference for A is given to ethylene,1,2-propylene or 1,2-butylene groups.

The variable Z is in particular C₁- to C₄-alkylene groups such asmethylene, 1,2-propylene, 1,2-butylene, 1,3-butylene or 2,3-butylene,C₅- to C₆-cycloalkylene groups such as 1,3-cyclopentylidene or 1,3- or1,4-cyclohexylidene, or C₆- to C₈-arylene or -arylalkylene groups suchas 1,3- or 1,4-phenylene, 2-methyl-1,4-phenylene or 1,3- or1,4-bismethylenephenylene.

However, the variable Z preferably represents polymethylene groups ofthe formula —(CH₂)_(n)— where n=2 to 8, in particular where n=2 to 6,i.e. in particular 1,2-ethylene, 1,3-propylene, 1,4-butylene,1,5-pentylene and 1,6-hexylene, but in addition also 1,7-heptylene and1,8-octylene.

When the variable m is 0, the parent cationic components of the fattyacid salts used according to the invention are generally, depending onthe sum (Σ) of all variables x¹, x² and x³, mixtures of mono-, di-and/or trialkanolamines or pure trialkanolamines. Examples of suchalkanolamines include monoethanolamine, diethanolamine, triethanolamine,monoisopropanolamine, diisopropanolamine, triisopropanolamine and alsotheir corresponding mixtures. Within this group, the oleic acid salt oftriethanolamine [(x¹+x²+x³)=3; A=ethylene] is of particular interest.

However, preference is given to the variable m being the number 1 or 2.When m=1, the parent molecules are partially and/or completelyalkoxylated alkylenediamines such as 1,2-ethylenediamine,1,3-propylenediamine or 1,4-butylenediamine. When m=2, the parentmolecules are usually partially and/or completely alkoxylateddialkylenetriamines such as di(1,2-ethylene)triamine,di(1,3-propylene)triamine or di(1,4-butylene)triamine. Within thisgroup, the bis-oleic acid salts ofN,N,N′,N′-tetrakis(2′-hydroxyethyl)-1,2-ethylenediamine (Σx=4) andN,N,N′,N′-tetrakis(2′-hydroxypropyl)-1,2-ethylene-diamine (Σx=4) andalso the tris-oleic acid salts of di(1,2-ethylene)triamine reacted withfrom 4 to 5 mol of ethylene oxide or 1,2-propylene oxide are ofparticular interest.

However, it is also possible that higher homologs of thealkylenediamines and dialkylenetriamines mentioned, for exampletriethylenetetramine (m=3), tetraethylenepentamine (m=4) orpentaethylenehexamine (m=5), may be the parent amine components for thefatty acid salts used according to the invention.

In a preferred embodiment, the number x, i.e. the sum of x¹, x², X³ andX⁴ (Σx), of alkylene oxide units (OA) introduced per amine molecule isdependent upon the number of N—H bonds in the parent amine and maycorrespond to the number of N—H bonds (Σx=m+3). However, it is alsopossible for more or fewer OA units to be incorporated. In the case ofgreater than stoichiometric incorporation, a preferred upper limit is athreefold alkoxylation per N—H bond [300% of (m+3)] with regard to theproperties of the resulting fatty acid salts. In the case of less thanstoichiometric incorporation, a preferred lower limit is an average 50%alkoxylation [50% of (m+3)]; in this case, there are usually mixtures ofspecies having differing degrees of alkoxylation.

In a particularly preferred embodiment, the sum (Σ) of all variables xhas a value of from 75% to 125% of (m+3).

The fatty acid salts of the general formula II can typically be preparedeasily by alkoxylating the parent amines by customary methods andsubsequently neutralizing with the fatty acids of the formula RCOOH.

When C₂- to C₄-alkylene oxides are used, the alkoxylation for theintroduction of the first alkylene oxide unit into the N—H bond isadvantageously carried out in the presence of small amounts of water(usually from 0.5 to 5% by weight, based on the amount of amine used)without catalyst at temperatures of from 80 to 140° C. and, for theintroduction of further alkylene oxide units, with the exclusion ofwater in the presence of basic catalysts such as alkali metalhydroxides, e.g. sodium or potassium hydroxide, at temperatures of from100 to 150° C.

The neutralization is generally effected by heating the alkoxylatedamine obtained in this way with the appropriate stoichiometric orslightly less than stoichiometric amount (i.e. from 90 to 100%, inparticular from 95 to 100%, of theory) of fatty acid to temperatures offrom 30 to 100° C., in particular from 40 to 80° C., for a period offrom 15 minutes to 10 hours, in particular from 30 minutes to 5 hours.The neutralization reaction should be conducted in such a way that nocarboxylic ester fractions occur in the product. In many cases, both thealkoxylated amine and the fatty acid may be used as liquids, which makesthe reaction to the corresponding fatty acid salt particularly simple.The sequence of addition of alkoxylated amine and fatty acid isuncritical, i.e. either the alkoxylated amine may be initially chargedand the fatty acid added or the fatty acid may be initially charged andthe alkoxylated amine added.

However, it is also possible in principle to add the alkoxylated amineand the fatty acid as individual components to the additive concentratesor to the mineral oil products and to allow the salt formation to takeplace there.

Other useful components B for the additive mixtures according to theinvention are long-chain carboxylic acids, esters thereof or mixtures ofsubstances which comprise at least one of these components.

For the purpose of the present invention, long-chain carboxylic acidsencompass saturated and unsaturated mono- or polycarboxylic acids havingfrom 4 to 50 carbon atoms, preferably from 8 to 24 carbon atoms. Whenthe carboxylic acids are present in dimerized form, the carbon number iscorrespondingly doubled. Polycarboxylic acids according to the inventionpreferably comprise from 2 to 4 carboxyl groups. Unsaturated carboxylicacids according to the invention comprise one or more, preferably one,two or three, in particular noncumulated, double bonds.

Preferred examples of saturated or unsaturated long-chain monocarboxylicacids are the saturated or unsaturated C₈-C₂₄-monocarboxylic acidsspecified in connection with the above definition for the compound ofthe formula II.

Examples of suitable polycarboxylic acids include saturated andunsaturated dicarboxylic acids, for example the dimerized variant ofoleic acid.

The carboxylic acids used may be of natural or synthetic origin. Theymay be used as a pure substance or as a substance mixture whichcomprises one or more of these carboxylic acids, optionally togetherwith further substances. A nonlimiting example is that of tall oil fattyacid mixtures. These typically comprise a mixture of saturated,monounsaturated and polyunsaturated C₁₈-carboxylic acids and varyingproportions of a hydrolyzable resin. Suitable products are described,for example, in WO-A-98/04656, which is incorporated herein by way ofreference.

The long-chain carboxylic esters which can be used according to theinvention can be prepared in a conventional manner by reacting the abovelong-chain carboxylic acids with mono- or polyhydric alcohols.

The alcohols present in the esters according to the invention arepreferably derived from straight-chain or branched C₁- to C₂₀-alkanesand bear from 1 to 8, for example from 1 to 4, hydroxyl groups. Cyclicalcohols having from 6 to 12 carbon atoms can likewise be used.

Preferred acyclic mono- or polyhydric alcohols comprise from 2 to 12,for example from 2 to 5, carbon atoms, are straight-chain or branchedand have from 1 to 4 hydroxyl groups. Nonlimiting examples aremonohydric alcohols such as methanol, ethanol and n- and isopropanol,and polyhydric alcohols such as glycol, glycerol, trimethylolpropane,pentaerythritol, sorbitol, mannitol, inositol, glucose and fructose. Thehydrocarbyl radical of the alcohols which can be used according to theinvention may optionally contain one or more heteroatoms such as oxygen,sulfur, nitrogen or phosphorus, in the carbon chain.

When polyhydric alcohols are used, these may be present in the estersaccording to the invention in partly or fully esterified form.Preference is given to mono- and diester esters.

Nonlimiting examples of esters which can be used are methyl esters ofthe above saturated or unsaturated monocarboxylic acids, and also thecorresponding esterification products of naturally occurring fatty acidsor fatty acid mixtures. Particular examples include mono- or diesters,for example glycerol monooleate, glycerol dioleate and glycerolmonostearate.

In the additive mixture according to the invention, component A andcomponent B are used in a weight ratio of preferably from 1:200 to 1:10,more preferably from 1:100 to 1:10 and in particular from 1:50 to 1:10.

The present invention further provides the use of the additive mixtureaccording to the invention for additizing fuel compositions, inparticular for improving the antifoam performance of a fuel composition.

Useful fuels are gasoline fuels and middle distillates, such as dieselfuels, heating oil or kerosene, although preference is given to dieselfuels.

The diesel fuels are, for example, crude oil raffinates which typicallyhave a boiling range of from 100 to 400° C. These are usuallydistillates having a 95% point of up to 360° C. or even higher. However,these may also be “Ultra Low sulfur Diesel” or “City Diesel”,characterized by a maximum 95% point of, for example, 345° C. and amaximum sulfur content of, for example, 0.005% by weight or by 95% pointof, for example, 285° C. and a maximum sulfur content of 0.001% byweight. In addition to the diesel fuels obtainable by refining, thoseobtainable by coal gasification or gas liquefaction (“gas to liquid”(GTL) fuels) are also suitable. Mixtures of the abovementioned dieselfuels with renewable fuels, such as biodiesel, are also suitable.

Particular preference is given to using the additive mixture accordingto the invention for additizing diesel fuels having low sulfur contents,i.e. having a sulfur content of less than 0.05% by weight, preferably ofless than 0.02% by weight, in particular of less than 0.005% by weightand especially of less than 0.001% by weight, of sulfur.

The present invention also provides a fuel composition comprising amajority of a hydrocarbon fuel and an effective amount of the additivemixture according to the invention and optionally at least one furtheradditive. With regard to suitable fuels, the same applies as was statedpreviously.

The additive mixture according to the invention is preferably present inthe fuel in an amount of from 1 to 1000 ppm by weight, more preferablyfrom 20 to 300 ppm by weight and in particular from 50 to 150 ppm byweight, based on the total amount of the additized fuel.

The present invention further provides an additive concentratecomprising the additive mixture according to the invention, at least onediluent and also optionally at least one further additive.

Examples of useful diluents include the fractions obtained in crude oilprocessing, such as kerosene, naphtha or brightstock. In addition,aromatic and aliphatic hydrocarbons and alkoxyalkanols are suitable. Inthe case of middle distillates, in particular in the case of dieselfuels, preferably used diluents are naphtha, kerosene, diesel fuels,aromatic hydrocarbons such as Solvent Naphtha heavy, Solvesso® orShellsol®, and also mixtures of these solvents and diluents.

The additive mixture according to the invention is present in theconcentrate in a concentration of from 0.1 to 80% by weight, morepreferably from 0.1 to 60% by weight and in particular from 15 to 50% byweight, based on the total weight of the concentrate.

Useful additives which may be present in the fuel or concentrateaccording to the invention in addition to the additive mixturesaccording to the invention, in particular for diesel fuels, includedetergents, corrosion inhibitors, dehazers, demulsifiers, othercustomary antifoams, antioxidants, metal deactivators, multifunctionalstabilizers, cetane number improvers, combustion improvers, dyes,markers, solubilizers, antistats, lubricity improvers, additives whichimprove the cold properties such as flow improvers (“MDFI”), paraffindispersants (“WASA”) and the combination of the two last-mentionedadditives (“WAFI”). Useful additives are described, for example, inUllmann's Encyclopedia of Industrial Chemistry (1990) Vol. A 16, p. 719ff., which is incorporated herein by way of reference.

The customary antifoams include the polysiloxanes mentioned at theoutset, acylated polyamines and their mixtures with different N-acylcompounds such as polyalkenylsuccinamides.

The synergistically effective combination of components A and B in theadditive mixture according to the invention leads to a distinctimprovement in the antifoam performance of fuels additized by itcompared to prior art additives.

The examples which follow are intended to illustrate the invention,without restricting it.

EXAMPLES

The tests described hereinbelow were carried out with the followingfuels:

-   diesel fuel to DIN EN 590 having a sulfur content of 48 ppm: Diesel    I-   diesel fuel to DIN EN 590 having a sulfur content of 15 ppm (ULSD):    diesel II-   diesel fuel to DIN EN 590 having a sulfur content of 4 ppm (MK1):    diesel III-   blend of 5% of biodiesel in 95% of diesel I: blend I-   blend of 8% of ethanol in 91% of diesel I (1% stabilizer package):    blend II-   gas to liquid fuel: GTL-   blend of 20% of GTL in 80% of diesel I: blend III

The lubricity improvers used were the following products:

-   Lubricity I: Product prepared according to Example 1-   Lubricity II: Tall oil fatty acid mixture obtainable under the trade    name Kerocom LA 99 from BASF AG-   Lubricity III: Fatty acid ester mixture using glycerol monooleate as    the main component.

An antifoam used is a polysiloxane derivative which is customary on themarket and referred to by the term antifoam.

EXAMPLE 1 Synthesis of a Lubricity Improver (Lubricity I)

58.4 g (0.2 mol) ofN,N,N′,N′-tetrakis(2′-hydroxypropyl)-1,2-ethylenediamine (obtained from1,2-ethylenediamine and 4 mol of propylene oxide in the presence of 3%by weight of water based on the amount of amine used) was heated to60-80° C. and admixed with 110.4 g (0.4 mol) of oleic acid within 2hours with stirring. The pH did not fall below 7. Finally, the stirringwas continued for another 2 hours. The product obtained had an N-titerof 2.39 mmol/g.

EXAMPLE 2 Tests for Determining the Antifoam Performance

The determination of the antifoam performance was carried out inaccordance with the BNPe test according to Standard NF M 07-075.

The additized fuels or blends were obtained by adding the abovementionedcombinations of 5 mg/kg of antifoam and 120 mg/kg of lubricity improverLubricity I to III in each case. In the table which follows, the valuesdetermined in each case for the foam volume and the foam degradationtime in dry fuels are listed. Foam Foam Lubricity volume degradationFuel Antifoam improver [ml] time [s] Diesel I 0 0 120 63 Diesel II 0 0115 46 Diesel III 0 0 110 35 Blend I 0 0 110 42 Blend II 0 0 100 40 GTL0 0 115 57 Blend III 0 0 115 60 Diesel I Antifoam 0 60 14 Diesel IIAntifoam 0 55 15 Diesel III Antifoam 0 50 13 Blend I Antifoam 0 60 16Blend II Antifoam 0 50 12 GTL Antifoam 0 60 14 Blend III Antifoam 0 6014 Diesel I Antifoam Lubricity I 40 5 Diesel II Antifoam Lubricity I 356 Diesel III Antifoam Lubricity I 30 4 Blend I Antifoam Lubricity I 35 6Blend II Antifoam Lubricity I 30 4 GTL Antifoam Lubricity I 35 5 BlendIII Antifoam Lubricity I 35 5 Diesel I Antifoam Lubricity II 55 11Diesel II Antifoam Lubricity II 55 12 Diesel III Antifoam Lubricity II60 10 Diesel I Antifoam Lubricity III 60 13 Diesel II Antifoam LubricityIII 55 16 Diesel III Antifoam Lubricity III 50 13

The lubricity improvers alone had no positive influence on the foamingaction.

The combinations of antifoam and Lubricity I, II and III according tothe invention compared to the action of antifoam alone showed adistinctly improved antifoam performance at the same lubricity-improvingaction. Particularly outstanding results are achieved when lubricityimprovers of the lubricity I type are used.

1. An additive mixture consisting of a component A and a component B,where i) component A is at least one polysiloxane antifoam and ii)component B is at least one partially or completely neutralized fattyacid, a long-chain carboxylic acid, an ester of such a carboxylic acidor a mixture comprising at least one of these compounds.
 2. An additivemixture as claimed in claim 1, which comprises, as component A, at leastone polysiloxane of the general formula I

where the R radicals are each independently an R¹, R², R³, R⁴or R⁵radical where R¹ is an aromatic or saturated aliphatic hydrocarbonradical, R² is an organic polyol, R³ is a polyether radical, R⁴ is aphenol radical, R⁵ is an R² radical, except that some or all of thehydroxyl groups have been converted to diesters, diethers, acetalsand/or ketals,w=2+y+2z, y and z are each independently a number from 0 to 2 where thesum of y and z corresponds to a number from 0 to 2 and w+x+y+z=from 20to
 60. 3. An additive mixture as claimed in claim 2, wherein, incomponent A, R¹ is C₁-C₂₄-alkyl, C₃-C₂₄-cycloalkyl,C₄-C₂₄-alkylcycloalkyl, C₆-C₁₀-aryl or C₇-C₁₈-arylalkyl, R² is asaturated or unsaturated, branched or unbranched, aliphatic hydrocarbonradical which is substituted by at least two hydroxyl groups and isoptionally interrupted by one or more oxygen atoms, R³ is a polyetherradical which contains at least 50% by weight of copolymerized ethyleneoxide units and has a molecular weight of up to 1500, the quotient ofthe number of R¹ groups to the number of R² groups (R¹/R²) is from 3 to19 and the quotient of the sum of the number of R³, R⁴ and R⁵ groups tothe number of R² groups [(R³+R⁴+R⁵)/R²1 is from 0 to
 2. 4. An additivemixture as claimed in claim 1, wherein component B comprises at leastone fatty acid neutralized by at least one amine.
 5. An additive mixtureas claimed in claim 4, wherein component B comprises at least one fattyacid salt of the formula II

where R is C₇-C₂₃-alkyl or mono- or polyunsaturated C₇-C₂₃-alkenyl, eachof which are optionally substituted by one or more hydroxyl groups; A isC₂-C₈-alkylene; Z is C₁-C₈-alkylene, C₃-C₈-cycloalkylene, C₆-C₁₂-aryleneor C₇-C₂₀-arylalkylene; m is a number from 0 to 5; and x¹, x², x³ and X⁴are each independently a number from 0 to 24, and optionally at leastone further fatty acid RCOOH where R is as defined above.
 6. An additivemixture as claimed in claim 1, wherein component B comprises at leastone saturated or unsaturated mono- or polycarboxylic acid having from 4to 50 carbon atoms or at least one ester of such a carboxylic acid witha mono- or polyhydric alcohol having from 1 to 20 carbon atoms and from1 to 8 hydroxyl groups.
 7. An additive mixture as claimed in claim 1,wherein component A and component B are present in a weight ratio offrom 1:200 to 1:10.
 8. A method of additizing fuel compositionscomprising adding to a fuel composition an additive mixture as definedin claim
 1. 9. The method as claimed in claim 8 wherein the additivemixture improves the antifoam performance of a fuel composition.
 10. Amethod of improving the antifoam action of a polysiloxane antifoam infuel compositions comprising including in the polysiloxane antifoam atleast one partially or completely neutralized fatty acid, a long-chaincarboxylic acid, an ester of such a carboxylic acid or a mixturecomprising at least one of these compounds.
 11. A fuel compositioncomprising a majority of a hydrocarbon fuel and an effective amount ofan additive mixture as defined in claim
 1. 12. A fuel compositioncomprising a majority of a hydrocarbon fuel and an effective amount ofan additive mixture, which comprises i) as component A, at least onepolysiloxane antifoam and ii) as component B, at least one fatty acidpartially or completely neutralized by at least one amine, andoptionally at least one further additive.
 13. A fuel composition asclaimed in claim 11, wherein the fuel is diesel fuel, heating oil orkerosene.
 14. A fuel composition or the use as claimed in claim 13,wherein the diesel fuel is one obtainable by refining, coal gasificationor gas liquefaction, or a mixture thereof with renewable fuels.
 15. Anadditive concentrate comprising an additive mixture as defined in claim1 and at least one diluent.
 16. The fuel composition as claimed in claim12, wherein the fuel is diesel fuel, heating oil or kerosene.
 17. Themethod as claimed in claim 8, wherein the additive mixture is added to adiesel fuel, heating oil or kerosene.
 18. The method as claimed in claim10, wherein the polysiloxane antifoam is added to a diesel fuel, heatingoil or kerosene.